Method of seasoning sheets containing a solvent



UNITED STATES iFFicfE METHOD OF SEASONING SHEETS CONTAIN- ING A SOLVENT Gustavus J. Esselen, Swampscott, Mass, assignor to The Fiberloid Corporation, Indian Orchard, Mass., a corporation of Massachusetts No Drawing. Application October 24, 1931, Serial No. 570,978

3 Claims. (01. 18- 51) The present application is a continuation in precipitating the pyroxylin, and then drying out part of my former application, Serial No. 249,- the non-solvent. While a variety of liquids may 744, filed January 26, 1928, for Method and apbe employed for the non-solvent bath the liqparatus for making a continuous web. In that uid must be one which is miscible with the solapplication there is described a process of provent, if not in all proportions, then in certain 60 ducing a continuous sheet or web of pyroxylin proportions and under certain conditions. For by extruding under pressure through an orifice instance, toluol in the aromatic series of hydroa mix of pyroxylin containing a solvent such as carbons or carbon tetrachloride being completean alcohol (either ethyl or methyl) or an ester ly miscible with ethyl or methyl alcohol may be '10 such as ethyl acetate in the presence of camemployed as a non-solvent; or V. M. P. naphtha, 5 phor and setting the mix to form a self susso-called in the aliphatic series, which is miscitaining sheet by immersion in a bath of nonble in certain but not in all proportions, may solvent liquid. By solvent I mean a liquid also be used. These non-solvents are capable capable of forming with the other ingredients of of displacing the solvent without precipitating .16 the mix a colloidal solution; by non-solvent I the pyroxylin. V. M. P. naphtha is commonly 7 mean a liquid which is incapable of forming known as Varnish Makers Petroleum and is such a solution. characterized by the fact that it has a flash point My present invention is based on the discovery not lower than 100 F. While its properties that the treatment described, when applied to vary with the particular refining company, a

120 unseasoned sheets formed by any suitable proctypical sample shows a gravity of 47.6, an initial 75 ess, has the effect of seasoning them, i. e. removboiling point of 311 F., and an end point of ing the residue of solvent which persists tena- 411 F. ciously in them. In order to produce a seasoned sheet which It is well recognized that sheets of pyroxylin is transparent, it is essential that the process of .25 or other cellulose ester whether made by the soseasoning remove the excess solvent Without 0 called cake process, 1. e. by the formation of precipitating the pyroxylin out of the solid solublocks or cylinders from which sheets are sliced tion. It the solution is precipitated, changes in or by some other process require long seasoning physical properties occur, for instance, the stock to reduce the residual amount of solvent conbecomes cloudy and brittle. Drying, which is the 3G tained in the sheets to the required minimum. ordinary method of seasoning, removes the eX- 8. This seasoning has ordinarily been accomplished cess solvent without precipitating the pyroxylin. preferably by hanging the sheets in hot rooms. This result is accomplished more rapidly by the Of necessity this process of seasoning is slow, practice of the invention. ordinarily occupying a week or two according to In practice I also find it desirable to use a .35 the thickness of the sheet, its condition and the suiiicient quantity of the plasticizer employed in '9 conditions of treatment, and is expensive bethe pyroxylin to prevent any considerable extraccause of the equipment required and of the large tion of the plasticizer from the pyroxylin sheet amount of stock which is processed. during treatment.

I have discovered that certain liquids" Which In practising my invention I make the sheet 40 are non-solvents of pyroxylin have the property from a suitable mix containing nitrocellulose or L of displacing solvents of pyroxylin from a sheet; the like; a solvent such as ethyl alcohol (containand further that when the solvent has been dising if required a suitable denaturant) or methyl placed by the non-solvent, the non-solvent can alcohol or ethyl acetate; camphor or other suitbe removed by evaporation much more rapidly able plasticizer and any other ordinary ingredi- 45 than a solvent. For some reason unknown to ents employed in the manufacture of pyroxylin'l me, pyroxylin appears to be much less tenacious The mix is then formed into sheets in whatever of non-solvents than of solvents. way chosen. Thereafter, I treat the sheets with These discoveries have made possible an ena suitable non-solvent, for instance, a hydrocartirely new method of seasoning sheet Dyroxylin Icon of the aliphatic series. Suitable materials 151) which reduces the time required by many days. are naphtha of the grade known as V. M. P.

Speaking generally, my process consists in imnaphtha, gasoline, toluol or carbon tetrachloride. mersing the unseasoned sheets containing a con- These liquids have the property of dissolving siderable percentage of a solvent of pyroxylin in camphor though they do not dissolve nitrocellua bath composed of a non-solvent which is capalose and therefore tend to extract the camphor 5'5 ble of displacing the solvent, preferably, without from the sheet, reducing the camphor content. 7110 Accordingly, I use in the bath a suiiicient amount of camphor and maintain the strength at such a point that the bath will not extract camphor from the sheet to a material extent.

As an example, a suitable bath is made of V. M. P. naphtha and camphor in the proportion of 66 parts of camphor by weight to 100 parts of naphtha. For sheets having a thickness of 0.020 inches an immersion for an hour or'even less is sufficient to extract or displace from the sheet the residual solvent, i. e. the alcohol remaining in the sheet at the time the sheet is formed. After removal from the bath the sheets are dried in any suitable manner as for instance by passing them through a current of dry air. The time required for drying is relatively short and I find that the entire process of seasoning the sheet can be completed in less than eight hours instead of requiring a week as heretofore.

The herein described method embodying my invention produces a sheet having a surface which is at least as good as that of sheets produced by the methods heretofore employed and also results in the savings already described.

While I have described my invention as I practice it, in connection with the manufacture of pyroxylin sheets, I believe it to be applicable to sheets of other substances containing solvents.

I claim:

1. The process of seasoning a sheet of pyroxylin or the like containing alcohol which consists in treating the sheet with carbon tetrachloride to displace the alcohol and then drying out the carbon tetrachloride.

2. The process of seasoning a sheet of pyroxylin or the like containing alcohol, which consists in treating the sheet with V. M. P. naphtha to displace the alcohol and then drying out the V. M. P. naphtha.

3. The process of seasoning pyroxylin sheet material containing a solvent which consists in treating the sheet with a liquid selected from the group consisting of toluol, carbon tetrachloride, gasoline and V. M. P. naphtha to replace the solvent in the sheet, and then drying the sheet.

GUSTAVUS J. ESSELEN. 

